The objective of this research plan is to elucidate the dynamic aspects of cholesterol ester metabolism in the brain. Although present only in very small amounts in normal adult brain, esterified cholesterol is present in significantly increased amounts just prior to active myelination and is greatly increased during the process of pathological demyelination. Our previous studies indicated presence of one cholesterol-esterifying enzyme and three distinct cholesterol ester hydrolases. All of the four enzymes differ from each other in the subcellular distribution and developmental changes. The first phase of the proposal will concentrate on solubilization, purification, and characterization of these enzymes. We have been able to solubilize all of the three hydrolases with adequate recovery and stability. Further purification will be attempted. Particular attention will be focused on the effects of exogenous lipids on these enzymes. We have shown dramatic effects of added lipids on some of these enzymes. Relationship of these esterifying and hydrolytic enzymes with other nonspecific synthetase and esterases will be examined. Similarly, the possibility of the three distinct cholesterol esterases being distributed preferentially in different neural cells, neurons, astrocytes, and oligodendroglia, will be examined with bulk-isolated neural cells, and when pure enzymes become available, by immunohistochemical means. Such clarification of the enzymatic machinery involved in formation and degradation of cholesterol esters in the brain should provide the fundamental information necessary for understanding the metabolic role of cholesterol esters in the brain under normal and pathological conditions.